Exit after fatal errors in client-side compression code.

Exit after fatal errors in client-side compression code.

It looks like whoever wrote the astreamer (nee bbstreamer) code
thought that pg_log_error() is equivalent to elog(ERROR), but
it's not; it just prints a message.  So all these places tried to
continue on after a compression or decompression error return,
with the inevitable result being garbage output and possibly
cascading error messages.  We should use pg_fatal() instead.

These error conditions are probably pretty unlikely in practice,
which no doubt accounts for the lack of field complaints.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/1531718.1772644615@sss.pgh.pa.us
Backpatch-through: 15